Multi-stimuli-engendered radical-anionic MOFs: Visualization of structural transformation upon radical formation

Understanding the dynamic structural changes accompanying radical formation provides detailed insights into the design of stimuli-responsive redox-active materials. In this study, we develop a metal-organic framework (MOF) comprising a pi-acidic 1,4,5,8-naphthalenediimide (NDI)-based ligand and Nd3+, viz. X-DGIST-4 (X = synthesis temperature in degrees C, DGIST = Daegu Gyeongbuk Institute of Science and Technology). The reduction of the NDI moieties to the radical-anionic state (NDI center dot-) in 75-DGIST-4 can be triggered by various stimuli (heat, X-rays, and ultraviolet, visible, and infrared light), indicating the presence of structure-guided multiple electron transfer pathways. The single-crystal-to-single-crystal transformation of 75-DGIST-4 upon X-ray-induced radical formation reveals sequential structural changes. The solvothermally synthesized radical-anionic MOF, viz. 150-DGIST-4, offers a more complete structural understanding of the radical-anionic state. Importantly, the stabilization of radical-anionic NDI.- by adjacent benzoates allows this state to be visualized by single-crystal X-ray diffractometry; the pendant benzoate is twisted to optimize the electrostatic interaction between NDI and the benzoate phenyl group.

Automated summary

Understanding the dynamic structural changes accompanying radical formation provides detailed insights into the design of stimuli-responsive redox-active materials. In this study, a metal-organic framework (MOF) was developed, and the reduction of NDI moieties to the radical-anionic state was triggered by various stimuli, revealing multiple electron transfer pathways guided by structure.